How Is Wilms Tumor Staged?
The stage of a cancer describes how far it has spread. Your child’s treatment and prognosis (outlook) depend, to a large extent, on the cancer’s stage. Staging is based on the results of the physical exam and imaging tests (ultrasound, CT scans, etc.), which are described in How are Wilms tumors diagnosed?, as well as on the results of surgery to remove the tumor, if it has been done.
Children’s Oncology Group (COG) staging system
A staging system is a standard way for the cancer care team to sum up the extent of the tumor. In the United States, the Children’s Oncology Group staging system is used most often to describe the extent of spread of Wilms tumors. This system describes Wilms tumor stages using Roman numerals I through V (1 through 5).
The tumor was contained within one kidney and was removed completely by surgery. The tissue layer surrounding the kidney (the renal capsule) was not broken during surgery. The cancer had not grown into blood vessels in or next to the kidney. The tumor was not biopsied before surgery to remove it.
About 40% to 45% of all Wilms tumors are stage I.
The tumor has grown beyond the kidney, either into nearby fatty tissue or into blood vessels in or near the kidney, but it was removed completely by surgery without any apparent cancer left behind. Nearby lymph nodes (bean-sized collections of immune cells) do not contain cancer. The tumor was not biopsied before surgery.
About 20% of all Wilms tumors are stage II.
This stage refers to Wilms tumors that may not have been removed completely. The cancer remaining after surgery is limited to the abdomen (belly). One or more of the following features may be present:
- The cancer has spread to lymph nodes in the abdomen or pelvis but not to more distant lymph nodes, such as those inside the chest.
- The cancer has grown into nearby vital structures so the surgeon could not remove it completely.
- Deposits of tumor (tumor implants) are found along the inner lining of the abdominal space.
- Cancer cells are found at the edge of the sample removed by surgery, a sign that some of the cancer still remains after surgery.
- Cancer cells “spilled” into the abdominal space before or during surgery.
- The tumor was removed in more than one piece – for example, the tumor was in the kidney and in the nearby adrenal gland, which was removed separately.
- A biopsy of the tumor was done before it was removed with surgery.
About 20% to 25% of all Wilms tumors are stage III.
The cancer has spread through the blood to organs away from the kidneys such as the lungs, liver, brain, or bones, or to lymph nodes far away from the kidneys.
About 10% of all Wilms tumors are stage IV.
Tumors are found in both kidneys at diagnosis.
About 5% of all Wilms tumors are stage V.
The other main factor in determining the prognosis and treatment for a Wilms tumor is the tumor’s histology, which is based on how the tumor cells look under a microscope. The histology can be either favorable or unfavorable (anaplastic). These are described in more detail in What is Wilms tumor?
Last Medical Review: March 6, 2015 Last Revised: February 16, 2016